Microbes in Human Welfare

I would carry a sample of curd from home because it contains lactic acid bacteria (LAB) in very large numbers. These microbes can be easily seen under a microscope, and curd is a common household sample in which microbes are present.

Yes. Microbes release gases during metabolism. For example:
- In making dosa and idli dough, bacteria ferment the dough and release **CO$_2$, which makes the dough puff up.
- In bread making, yeast** (*Saccharomyces cerevisiae*) ferments the dough and produces **CO$_2$.
- In sewage digesters and biogas plants, methanogens produce gases like methane, CO$_2$ and H$_2$**.

You would find lactic acid bacteria (LAB) in curd. Their useful applications are:
- They convert milk into curd.
- They help **increase vitamin B$_{12}$ content and improve nutritional quality.
- In the stomach, they help check disease-causing microbes**.
- They are also involved in the fermentation of some food products.

Traditional Indian foods made with microbes include:
- Wheat: bread
- Rice: idli and dosa
- Bengal gram: foods made from fermented batter or products prepared using microbial fermentation
These foods are prepared by microbial fermentation, which helps in raising the dough and developing texture and flavour.

Microbes have played a major role by producing antibiotics, which are chemical substances that kill or retard the growth of disease-causing bacteria. For example, penicillin helped in controlling bacterial diseases like diphtheria, whooping cough and leprosy, and many other antibiotics have saved millions of lives.

The chapter states that Penicillin was discovered from the mould Penicillium notatum. Another commonly cited antibiotic-producing fungus is Penicillium chrysogenum. So, any two fungi used in antibiotic production are Penicillium notatum and Penicillium chrysogenum.

Sewage is the municipal waste water containing human excreta, organic matter and microbes. It can be harmful because it often contains pathogenic microbes and a large amount of organic waste. If released untreated into rivers and streams, it causes water pollution and increases water-borne diseases.

The key difference is:
- Primary treatment is mainly physical; it removes large and small particles by filtration and sedimentation.
- Secondary treatment is biological; useful aerobic microbes break down organic matter and reduce BOD.